Shelf unit



FIG. 1 is a top front and right side perspective view of a shelf unit, illustrating my new design;

FIG. 2 is a top plan view thereof;

FIG. 3 is a front elevational view thereof;

FIG. 4 is a left side elevational view thereof, the right side elevational view being a mirror image;

FIG. 5 is a rear elevational view thereof; and,

FIG. 6 is a bottom plan view thereof. 

The ornamental design for a shelf unit, as shown and described. 